Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, destructiveHint:false and openWorldHint:false, so safety is covered and the bar is lower. The description still adds non-obvious behavior: it discloses the return shape '{id, title, text, url}' despite there being no output schema, and notes ids must originate from search rather than arbitrary URLs. It does not cover error behavior for unknown/malformed ids, which keeps it from a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The core action is front-loaded in the first clause, and every subsequent clause adds distinct information (the three id types, read-only status, return shape). The three-part parenthetical is dense but information-bearing rather than filler, so it stays within a reasonable size for the amount of routing it does.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

One required parameter with full schema coverage, rich annotations, and no output schema — and the description fills the output gap itself by naming the returned fields and the per-type content. Nothing an agent needs to select or correctly invoke this tool is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the id format is already documented and the baseline is 3. The description goes slightly beyond the schema by mapping each prefix to the specific content it yields (brand fields, campaign fields, full help answer plus source page), which tells the agent what to expect from the single parameter rather than just its syntax.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (fetches) and resource (the full record behind a search result id), then enumerates the three id namespaces and exactly what each returns. The closing 'Not a web fetch — ids come from search' explicitly separates it from any web-fetch interpretation and from the sibling search tool, so an agent can identify it without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives clear usage context by tying the tool to ids produced by 'search' and explicitly rules out web URLs ('Not a web fetch'). That is a real when-to-use and when-not signal. It stops short of a 5 because it never routes the agent among the overlapping getters (get_brand_brief, get_brand_guide, get_post) for the same underlying data.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.